I thought it would be the closest to how I imagined, but you're quite right that I didn't explain that.
We already know the artificial nerve connection between ring and brain, so... I'll just skip that.
What I meant is that you cannot create items with too much detail or over-complicated structure. Such are decorative items: sculptures, statues, fancy metalwork and such. Complicated structures restriction: even if the user knows how (for example) a pistol works, he can't just imagine that he is holding the firearm and create it. Weapon parts are possible, but only separately and only with necessary materials and knowledge.
Oh, I found a better word already: spontaneous! (Is it really better ?_?)
St00pid example:
I'll stick to the popular sword for now. The weapon created is not actually a sword with hild and blade, but rather a blade forming on the user, in this case, the arm. To achieve this, the user must 'imagine' that the claw grows and is attached to his arm. The bots act accordingly to the signal and form the blade. Action of course is not instantaneous. The time of 'production' is determined by the mass of the item, of course.
Assume that enough nanobots are in reserve to move. The user 'sends the command' to the bots to rearrange into the shape of a sword (whatever type the user prefers from European style longswords, epรยฉe swords or even Eastern style blades). An epรยฉe sword would be ready in about 1 to 1,5 seconds. A katana sized sword would take about 3,5 seconds, because it has not only a blade but a dangerous edge as well. A LARGE blade, similar to those of double handed swords, could take up to 7 or 8 seconds.
This is merely an example. The user can create a duster or a small dagger even, or separate a knife from the reserves. Quality of the blade depends whether it was created hastily or with time to adjust minor details (surface, edge), but don't expect a blade with dragons and 'pwetty icons' engraved in it. The former can result in very poorly made weapons, while the latter can be almost or just as good as a hand-made piece.
I hope I was more reassuring than puzzling. ^______^"""